Orthopedic surgeons have relied upon the process of distraction osteogenesis to reconstruct and lengthen bones. This process may involve placing a vascularized piece of bone under tension, thereby inducing native bone formation via the creation of a bony reparative callus, which can then placed under tension to generate new bone. To effect distraction osteogenesis, a surgeon generally performs an osteotomy, thereby sectioning or segmenting the bone to be altered into more than one piece. As the bone heals, it can slowly and gradually expand over a period of time so that the blood vessels and nerve ends remain intact during the distraction process. For example, the bone may be extended a millimeter a day, often by performing two extensions of half a millimeter, for three or four weeks.
As the gap between the bone segments widens, the natural healing capacity of the body can fill the void with new bone and adjacent soft tissue. Once the desired bone formation is achieved, the area may be allowed to heal and consolidate. Often, the distraction osteogenesis device is then removed.
Known distraction osteogenesis devices may present numerous disadvantages. First, distraction osteogenesis devices are generally external, which may cause a number of problems or complications. Often, cumbersome metal rods and rings located external to an individual's skin are used to distract or separate bone segments. Individuals, and in particular small children, may fall and injure themselves on the protruding metal edges. Further, small children may complicate the distraction osteogenesis procedure by improperly adjusting the osteogenesis distraction device. The distraction osteogenesis device may require multiple entry points to an individual's skin and thus may create multiple scars. Distraction osteogenesis devices requiring multiple entry points may also increase the likelihood of infection due to the multiple openings in the individual's skin. Also, individuals undergoing the distraction osteogenesis procedure have to cope with an external device, which is not cosmetically appealing.
A second problem encountered with distraction osteogenesis devices regards customizing devices for individuals. Generally, a distraction osteogenesis device used for one individual would not be suitable for another. In distraction osteogenesis devices used in the craniofacial area, for example, distraction osteogenesis devices must be measured to fit specific surface areas of craniofacial bones. Also, individuals may have different amounts of bone caused by different types of birth abnormalities or accidents, thus requiring customized distraction osteogenesis devices due to limited bone.
Third, distraction osteogenesis devices are attached to bone segments in such a way that the point of fixation to the bone transfers force during activation. For example, a distraction osteogenesis device may be attached to a bone segment by a bone screw or rod, which transfers a substantial amount of force during activation or when the distraction osteogenesis device is exerting pressure between the bone segments. By having the bone screw transfer a substantial amount of the force during activation, the distraction osteogenesis device may be dislodged from the bone.
Fourth, distraction osteogenesis devices are activated using constant rates, which do not reflect the individual's healing abilities. Regardless of the age or condition of the individual, distraction osteogenesis devices are typically activated by widening the gap between bone segments 0.125 mm to 0.50 mm four times per day. This conventional activation rate results in bone growth as low as 20 mm in 20 days. Accordingly, an individual may have to be under constant medical supervision for up to 20 days. An individual could be an outpatient, but would need to return to the hospital four times per day for adjustments. Present distraction osteogenesis device activation techniques do not take into account an individual's ability to grow bone at a greater or lesser rate. By using this constant rate, bone may grow too quickly and lock the distraction osteogenesis device, or in the alternative, bone may grow too slowly, requiring a longer period of time that the distraction osteogenesis device is necessary.
Therefore, it is desirable to provide a distraction osteogenesis device suitable for indexed osteotomy following permanent implantation beneath an individual's skin or soft tissue. The permanently implanted distraction osteogenesis device then could be permanently positioned within an individual, thereby eliminating the need for surgery in removing the device, including the associated risks and costs. The distraction osteogenesis device then would be more cosmetically appealing and reduce the likelihood of infection, injury and/or scarring. Further, it is desirable to have a distraction osteogenesis device that does not have to be customized for each individual. Manufacturing and medical costs would then be substantially reduced by using a standard distraction osteogenesis device and method, rather than customizing distraction osteogenesis devices and methods for each individual. The distraction osteogenesis device also should be affixed to bone in such a way that a substantial amount of the force used in activation is not transferred through a fastening device (i.e., screw, pin or rod). Finally, the distraction osteogenesis device should be activated at an optimal rate for an individual's bone growth.
To further improve the distraction osteogenesis procedure, it would desirable to enhance bone healing and bone remodeling so that the segmented bone can be expanded more rapidly over time and at the same time add increased strength and stability to the newly formed bone.
The foregoing shows a need for devices and methods for distraction osteogenesis involving a distractor suitable for indexed osteotomy following permanent implantation into bone, preferably alveolar bone.